This invention relates to a recording apparatus and method, a recording head and a circuit for driving the recording head. More particularly, the invention relates to an apparatus and method, in which an image is recorded by causing a recording head to perform scanning motion, the recording head and a circuit for driving the recording head.
In a head having a number of recording elements, generally the recording elements are divided into a plurality of blocks and the blocks are driven in time-sharing fashion. The reason for this is that such a method of drive reduces the number of recording elements that are driven simultaneously. As a result, there is a smaller voltage drop in common wiring, which voltage drop is attendant upon a decrease in current value. In addition, a smaller power supply capacity is sufficient. Furthermore, in an ink-jet printer, mutual pressure interference (crosstalk) between nozzles serving as the recording elements can be reduced.
FIG. 8 is a block diagram of a circuit arrangement which uses such driving by time division. An M-bit driver is a functional element that controls passage of current to the recording elements, where M corresponds to the number of nozzles. An M-bit shift register is a circuit in which image data is arranged and stored in correspondence with the recording elements. Image data on a signal line S.sub.-- IN which arrives in synchronization with an image-data transfer clock SCLK enters the shift register. When M-bit data is transferred, a LAT signal is supplied, whereby an M-bit latch latches the M-bit data that has been stored in the M-bit shift register.
The M-bit data is inputted into AND gates, which take the logical product between this data and block-enable selection signals BE1.about.BEN of N bits from the M-bit driver. More specifically, by applying drive signals divided in terms of time to the block-enable selection signals BE1.about.BEN, time division on the basis of division by N can be achieved.
In a case where the number of time divisions is large, it is known to provide a block-enable selection decoder in order to reduce the number of block selection signals. In a case where N is set as the simultaneous drive number with respect to the number M of nozzles, an arrangement can be adopted using a block-enable selection decoder having an M/N-bit output. The relation between the value of M/N and the number X of terminals of the blockenable selection decoder is as follows in terms of the decoder construction: EQU number of time divisions NN=M/N=2.sup.x
The number of enable terminals can be reduced from M/N to X.
FIG. 7 illustrates an example of a case in which the number of time divisions (the number of blocks) is 16. A head having 128 nozzles is divided into 16 blocks (BE1.about.BE16) by a 4to16 decoder using signals A.about.D of four input bits. By entering a nozzle drive signal HENB besides BE1.about.BE16, the degree of freedom of the driving waveform is raised. The signals BE1.about.BE16 and HENB are supplied to segments (nozzles), shown in FIG. 8, by AND gates that take the AND with image data stored by a latch circuit. By virtue of this block-enable selection decoder, 16 drive signals that were required can be reduced to five drive signals.
However, when a head having nozzles arranged on the same straight line is driven by time division block by block, the carriage mounting the recording head is moved in the scanning direction, as a result of which the dot-impact positions are shifted. This shift or deviation in dot-impact position caused by time division is a problem particularly in a head having a large number of time divisions, such as a head having the above-mentioned block-enable selection decoder.
Accordingly, successively dispersed drive disclosed in Japanese Patent Publication No. 3-208656 has been proposed. According to this drive, the deviation in printing caused by time division is eliminated by tilting the head.
This will be described with reference to FIG. 9. This illustrates an example of successively dispersed drive in a case where the number N of time divisions is 16.
In FIG. 9, the bold line indicates the tilt of the recording head. The numerals inside the circles indicate the numbers of nozzles which discharge ink drops that impact at these positions.
The 1st through 16th nozzles corresponds to a first group, the 17th through 32nd to a second group, and the 33rd through 48th to a third group. There are eight groups in all (for a total of 128 nozzles).
The leading nozzle (17th nozzle) of the second group is situated above the immediately preceding vertical column of dots with respect to the leading nozzle (first nozzle) of the first group. Similarly, the leading nozzle (33rd nozzle) of the third group is situated above the column two columns ahead with respect to the leading nozzle of the first group. In other words, each group is so arranged as to record dots (16 dots in this case) on the preceding column with respect to the preceding group.
Accordingly, in a case where an image is recorded by causing the head to perform scanning motion, the second group records an image of (n-1)th columns while the 16 nozzles of the first group are recording an image of an n-th column from the beginning of a band image. Similarly, the third group records an image of the (n-2)th column.
This will be described in greater detail. As shown in the timing chart of FIG. 9, the leading nozzle of the first group and the leading nozzle of the second group (and of the 3rd through 8th groups) are driven at the same time, after which the succeeding nozzles are driven in order, i.e., in the order of the second nozzle, third nozzle of each group and so on. Hereinafter, a set of nozzles driven simultaneously will be referred to as "block".
Accordingly, a binary signal for driving the recording head in this case sets 16 bits in a different vertical column group by group.
This recording head is attached at an inclination .theta. with respect to the carriage scanning direction. The value of .theta. is defined as follows: EQU .theta.=arctan (1/16)=3.6.degree.
which depends upon the nozzle interval (16 in FIG. 9) at which nozzles are driven at the same time. (The dot interval in the horizontal direction is assumed to be equal to the dot interval in the vertical direction.) The optimum block interval in this case (the maximum block interval of time division) is given by the following equation: EQU TB=T/NN (1)
where T represents the drive period (the time required for drive of all nozzles to be completed) and NN is the number of time divisions.
More specifically, if the block interval (ENB signal interval) is TB, as shown in FIG. 9, a printing deviation caused by time division will be eliminated since the head is tilted by the amount of the shift in impact position owing to time division. In such successively dispersed drive, there is no deviation in printing caused by time division. Therefore, it is desired that the number of time divisions be as large as possible. In general, the number of input signals necessary for time division is reduced by the block-enable selection decoder, etc.
Many recording apparatus such as printers having a variety of printing speed modes. For example, a portable printer generally has three types of printing speed modes, namely HQ (high quality), HS (high speed) and battery drive. Consider the number of time divisions when the drive frequency for HQ is 5 kHZ (period T=200 .mu.s), the drive frequency for HS is 10 kHZ (period T=100 .mu.s) and the drive frequency for battery drive is 2.5 kHZ (period T=400 .mu.s).
If the necessary driving pulse width of the head (the minimum pulse width that must be provided) is 10 .mu.s, the maximum number of time divisions in the above-mentioned modes is 20 for HQ, 10 for HS and 40 for battery drive, based upon Equation (1).
In this case, the number of time divisions with the conventional circuit arrangement of the kind shown in FIG. 7 is ten for the HS mode, which has the smallest number. (The reason for this is that if the number of time divisions exceeds ten, the necessary driving pulse width 10 .mu.s of the head cannot be satisfied in the HS mode.)
Consequently, the merits of time-division drive mentioned above diminish. In particular, in battery drive, the design must be such that four times as much instantaneous current will flow in comparison with a circuit for which the number of time divisions is 40.
Similarly, in a case where the same head is used in a variety of recording apparatus, the necessary printing frequency differs depending upon the particular application but the number of time divisions of the head must be decided while assuming the highest printing drive frequency.
Therefore, since the simultaneous drive current becomes large, the common wiring must be widened in order to reduce the voltage drop and the number of contact terminals must be increased. Furthermore, it is necessary to enlarge the capacity of the power supply. The result is a larger apparatus and a rise in cost.
In successively dispersed drive, the inclination of the head must be enlarged if the number of divisions is small. In a recording apparatus of the exchangeable head type, therefore, it is difficult to achieve contact between the head and apparatus. Consequently, there is a decline in contact reliability and a complex contact design is required.
Usually, the same head is made to perform printing at various drive frequencies depending upon the printing mode and printing apparatus. However, in a head having a block-enable selection decoder, the number of time divisions must be decided upon assuming the highest printing frequency. Another problem is that "shifted time-division drive" cannot be carried out.